CHAP. IX.] 



TIDES 



229 



tides are regular or not, and any assumption would probably Interpo- 

 end in very erroneous results. Height of 



In a case where only the high and low waters on any day Tide, 

 are obtained, the height of the tide, at times between, is best 

 to be got at by drawing a curve in the imagined course of the 

 tide, after the manner of Fig. 61 ; the height on the pole at 

 any time can then be taken from this, and a table of reduction, 

 formed for the day. 



Thus, in Fig 62, where we have only got the times and heights 

 at high and low water on that day, viz., H. W. at VI. 50, mark 

 on pole 15 feet 7 inches ; L. W. at I. 10, mark on pole 8 feet. 



On a piece of paper, either ruled in squares for the purpose, 

 or on ready-printed squared paper, which is very useful to 



Fig. 62. 



have by one for these like occasions, we draw a curve after 

 the fashion shown. Then, supposing our datum for reduc- 

 tion to have been settled as 4 feet on the pole, our table of 

 reduction for the day will stand as follows : 



